Many postmenopausal women take hormonal therapy medicine – either an aromatase inhibitor or tamoxifen – after breast cancer surgery and other treatments for hormone-receptor-positive, early-stage breast cancer. Hormonal therapy medicine can reduce the risk of the cancer coming back (recurrence).

A new analysis of results from the BIG 1-98 trial found that the aromatase inhibitor Femara (chemical name: letrozole) improved both disease-free survival (living without the cancer growing) and overall survival (living whether or not the cancer grew) compared to tamoxifen in postmenopausal women diagnosed with estrogen-receptor-positive, HER2-negative breast cancer.

The benefits of Femara over tamoxifen were most notable in treating lobular breast cancer compared to ductal breast cancer. Femara was also better at treating luminal B breast cancers with a high level of the protein Ki-67, which helps breast cancer cells grow.

The study, "Relative effectiveness of letrozole compared with tamoxifen for patients with lobular carcinoma in the BIG 1-98 trial," was presented at the 2012 San Antonio Breast Cancer Symposium.

Lobular breast cancer is breast cancer that begins in the milk-producing lobules, which empty out into the milk ducts that carry milk to the nipple. Ductal breast cancer is breast cancer that begins in the milk ducts. Ductal breast cancer is the most common type of breast cancer – about 80% of all breast cancers start in the milk ducts.

Luminal B breast cancer is hormone-receptor-positive, HER-positive breast cancer, or HER2-negative with high levels of Ki-67. Hormone-receptor-positive, HER2-negative breast cancer with low levels of Ki-67 is called luminal A breast cancer.

In the BIG 1-98 trial, more than 8,000 postmenopausal women diagnosed with early-stage, hormone-receptor-positive breast cancer were randomly assigned one of four treatments after surgery:

5 years of Femara

5 years of tamoxifen

2 years of tamoxifen then 3 years of Femara (sequential therapy)

2 years of Femara then 3 years of tamoxifen (sequential therapy)

Half the women were followed for more than 8 years; the others for shorter times. The researchers then compared the outcomes of the different treatments.

The researchers found that women who got 5 years of Femara had:

better disease-free survival

better overall survival

compared to women who got 5 years of tamoxifen.

Because lobular breast cancer is less common – about 10% of breast cancers start in the lobules – the researchers decided to see if Femara offered any benefits specifically for lobular breast cancer.

So they compared the outcomes of the 324 women in the BIG 1-98 study diagnosed with lobular breast cancer to the 2,599 women diagnosed with ductal cancer who got only Femara or only tamoxifen.

All the cancers were estrogen-receptor-positive and HER2-negative, but there were differences in Ki-67 protein levels:

55.3% of the ductal cancers had low levels of Ki-67 (luminal A cancer)

46.7% of the ductal cancers had high levels of Ki-67 (luminal B cancer)

73.1% of the lobular cancers had low levels of Ki-67 (luminal A cancer)

26.9% of the lobular cancers had high levels of Ki-67 (luminal B cancer)

This difference in disease-free survival for lobular breast cancer was significant, which means that it was likely because of the difference in treatment and not just due to chance.

Of all the women diagnosed with luminal A breast cancer, women diagnosed with lobular breast cancer treated with tamoxifen had the worst outcomes compared to women diagnosed with ductal breast cancer treated with Femara or tamoxifen and women diagnosed with lobular breast cancer treated with Femara.

Of all the women diagnosed with luminal B breast cancer, women treated with tamoxifen had worse outcomes than women treated with Femara no matter if they had ductal or lobular breast cancer. Women diagnosed with lobular breast cancer treated with tamoxifen had the worst outcomes in this group.

While these results are interesting, more research is needed to confirm that Femara is a better choice to treat lobular breast cancers and luminal B breast cancers.

Research shows that an aromatase inhibitor such as Femara is the best hormonal therapy medicine after breast cancer surgery for postmenopausal women diagnosed with early-stage, hormone-receptor-positive breast cancer. Still, tamoxifen can be a good choice, depending on a woman’s unique situation and the cancer’s characteristics.

When you’re deciding on a treatment plan after breast cancer surgery, keep two things in mind:

Every woman responds differently to treatment. What works for you may not work for someone else.

Your treatment plan isn't written in stone. You can always switch medicines if another treatment has greater benefits and fewer side effects.

If you’re a postmenopausal woman being treated for hormone-receptor-positive, early-stage breast cancer, ask your doctor about the cancer’s characteristics. Is it luminal A or luminal B? Did it start in the lobules or the milk ducts? If the cancer is lobular and/or luminal B, you may want to ask your doctor about this study and whether Femara is a good hormonal therapy option for you. Armed with the most up-to-date information, you can make the best decisions about a treatment plan that’s right for you.